Technical Field
The present disclosure relates to the fabrication of nanometer-sized integrated circuit field effect transistor (FET) devices and, in particular, to devices that incorporate quantum dot films to control electrical characteristics of the devices.
Description of the Related Art
As technology nodes for integrated circuits scale below 10 nm, maintaining precise control of various electrical characteristics in bulk semiconductor devices becomes increasingly more challenging. Bulk semiconductor devices include, for example, metal-oxide-semiconductor field effect transistors (MOSFETs). A MOSFET is a three-terminal switching device that includes a source, a gate, and a drain. MOSFETs are interconnected by a network of wires through contacts to each of the source, drain, and gate terminals.
When a voltage exceeding a certain threshold voltage (Vt) is applied to the MOSFET gate, the device switches on so that an electric current flows through a channel between the source and the drain. Thus, improving device performance depends on the ability to control Vt. The value of Vt depends, in part, on the characteristic energy band structure of the semiconductor material and, in particular, on a characteristic band gap which represents the amount of energy needed to boost a valence electron into the conduction band, where the electron can participate as a charge carrier in the channel current. Altering the semiconductor crystal is thus a way to control the band gap and in turn, the threshold voltage.
In conventional devices, the semiconductor crystal was typically altered, for example, by doping the crystal with ions in the source and drain regions of a MOSFET. In a silicon device, for example, the doping process alters the crystal structure by substituting ions for the silicon atoms. Improvements in device performance (e.g., switching speed) traditionally has been largely dependent upon control of doping concentrations in the source and drain and the locations (e.g., depth profiles) of the dopants in the substrate after ion implantation and/or after annealing implanted regions at high temperatures. In recent years, alternative methods of introducing dopants without damaging the substrate have included in-situ doping during a process of epitaxial crystal growth at the surface of the substrate.